Iowa Conservation Practices:
Historical Investments, Water
Quality, and Gaps
(Final progress report)
February, 2007
(revised version)
October, 2007
1
Project Overview
Goals
1. What conservation practices are currently in
place in Iowa, what is their coverage, and
what is the cost of these practices?
2. What are (and have been) the effects of this
investment on water quality?
3. What would it take to improve water quality
to obtain specific standards?
3
Surveys Used
NRI
CTIC
Description
USDA Survey
Reported findings from the USDA’s Crop
Residue Management Survey
Coverage
Contour Farming
Contour Stripcropping
Filter Strips
Grassed Waterways
Terraces
Erodibility Measures
CRP
Tillage Practices
Years
1997
2004
Nature of Survey
statistically based survey.
Data were collected using a variety of imagery,
field office records, historical records and data,
ancillary materials, and a limited number of onsite visits
“best estimates” of district conservationist are
combined with Cropland Transect Surveys
Positives
1. Records the total coverage of the practices
(both those that received financial assistance
and those that were installed voluntarily
without funding).
1. Records the total coverage of the practices
(both those that received financial assistance
and those that were installed voluntarily
without funding).
Negatives
1. Conservation practice usage is calculated
from a sample and so assumptions are made
about the population.
1. Aggregate data (at the county level) that
cannot be directly used in water quality
modeling.
5
Statewide average cost
Practice
Statewide Average Cost
Grass Waterway
$2,127/acre
Terrace
$3.57/ft
Water & Sediment Control Basin
$3,989/structure
Grade Stabilization Structure
$15,018/structure
Filter Strip
$116.83/acre
Contour Buffer Strip
$78/acre
Riparian Forest Buffer
$486/acre
Wetland Restoration
$245/acre
Nutrient Management
$4.09/acre
Contour Farming
$6/acre
No Till
$17.94/acre
Continuous CRP
$142/acre
General CRP
$97/acre
6
Statewide Coverage
Practice
Statewide Coverage
Grass Waterway (NRI)
2,225,900 acres
Terrace (NRI)
1,997,900 acres
Contour Stripcropping (NRI)
236,800 acres
Contour Farming (NRI)
5,148,200 acres
Mulch Till (CTIC)
8,290,000 acres
No Till (CTIC)
5,220,000 acres
CRP (CRP program)
1,894,488.2 acres
7
Total Costs of the Practices
Practice
Terraces
Cost
$692,147,676
Grassed Waterways
$95,090,424
Contour Farming
$30,889,200
Contour Stripcropping
No-Till
Much Till
CRP
$37,194,949
$3,552,000
$104,308,740
$82,861,900
$397,490,205
$175,878,365
 The first two practices are structural practices.
 Divide the installation costs over the lifespan of the practices (terrace:
25yrs, GW: 10 yrs), then the sum of annual payment is: $37,194,949.
The cost numbers for the rest of the practices are annual payments.
Then the total annual costs would be:
$37.2million + $397.5million = $434.7
8
13 Iowa Watersheds
10
% Improvement due to Existing Practices
Flow
Nitrate
Org N
Min P
Org P
Total N
Total P
Boyer
-8
23
56
45
50
38
48
Des Moines
-8
14
39
29
37
15
33
Floyd
-4
19
42
41
44
25
42
Iowa
-5
10
41
0
40
13
25
Little Sioux
-7
20
52
40
50
24
47
Maquoketa
-1
8
42
37
42
17
39
Monona
-3
15
49
54
61
26
58
Nishnabotna
-3
21
52
45
47
33
46
Nodaway
-2
28
56
49
51
37
50
Skunk
-6
14
46
40
44
21
42
Turkey
-5
5
38
30
37
18
34
Upper Iowa
-3
7
48
38
47
18
45
Wapsipinicon
-8
6
46
34
45
11
40
11
What would it take to improve
water quality?

Numerous conservation practices could be
implemented on any field, each with different
levels of effectiveness and costs

Solving for the least-cost solution requires
comparison among a very large number of
possible land use scenarios
13
Approach

Evolutionary algorithms provide one search
strategy

mimic the power of evolution, which, in effect,
is a method of searching for solutions among an
enormous amount of possibilities (Mitchell,
1999)

Outline basic idea only
15
Pareto Optimality

Point A is not clearly
preferred to point B (since
B has lower costs, but
higher pollution)

Point C ought to be
preferred to point D (since
D exhibits both lower costs
and lower pollution levels)

We try to identify a frontier
like ABC and then push it
toward the origin
16
Flow diagram
18
Land use options considered
1. Land Retirement
2. Corn-Soybeans, Conventional Tillage
3. Corn-Soybeans, No-Till
4. Corn-Soybeans, 20% Fertilizer Reduction
5. Contouring
6. Terracing
7. Combinations (as sensible) of above
practices
20
State-wide results


Apply the evolutionary algorithm to the 13 watersheds
A challenging task, given the number of HRUs and current
computing capacity




Results presented are based on over 91 days of CPU time
Over 116,000 SWAT model runs
Overall, the algorithm is able to identify scenarios which result in
significant reductions in loadings of nitrates and phosphorus
relative to baseline
Results must be interpreted with caution:

it is possible that better solutions could be identified, given enough CPU
time
23
State-wide results: P-N targeting
Watershed
Boyer
P loading,
kg
Actual P
loading,
% of
baseline
P concentration,
mg/L
Gross Cost, $
Net cost, $
N
loadings,
in % of
baseline
N
concentration,
mg/L
648,398
59.7
0.742
14,950,585
4,708,885
66.2
2.232
1,482,270
58.387
0.129
190,010,000
145,910,600
75.9048
4.514
295,676
52.2
0.560
8,056,582
2,778,832
64.2
4.494
2,432,160
67.1
0.206
193,575,632
109,999,532
75.2
6.189
Little Sioux
800,924
57.5
0.491
33,142,350
11,949,650
64.2
3.617
Maquoketa
14,589
39.8
0.323
2,218,699
-15,780,401
60.6
3.682
200,116
60.3
0.546
7,753,342
-1,491,738
55.1
4.158
2,068,920
67.3
0.625
43,579,662
13,676,562
65.1
2.408
354,088
61.6
0.401
8,140,247
3,370,077
72.9
2.049
1,842,720
63.6
0.482
50,379,561
29,196,661
75.2
2.595
Turkey
981,900
71.3
0.381
17,057,490
1,707,090
74
2.999
Upper Iowa
130,640
60.5
0.100
11,038,459
3,740,489
75.8
1.635
Wapsipinicon
413,100
67.6
0.135
33,030,359
12,112,059
70
3.861
Des Moines
Floyd
Iowa
Monona
Nishnabotna
Nodaway
Skunk
30
State-wide summary of P-N
targeting




The total gross cost of implementing the management
scenarios is almost $613 million a year
The net cost is estimated to run just under $322 million
a year
Following the prescriptions of the algorithm for each
of the watersheds results in the state-wide reduction in
phosphorus loadings of over 36%
would simultaneously result in the state-wide reduction
in nitrate loadings of over 31%
31
Comparison of
selected watersheds: Des Moines
33
Nodaway
34
Scenario Maps
38
Distributions of options
(alleles) and practices
700
600
500
400
300
200
100
0
T
C
S
C
S
C
C
S
N
T
R
F
Ar
Te
ea
rra
C
T
ce
Te
d
A
rra
re
c
a
ed
C
S
R
N
F
T
Ar
C
Te
S
ea
rra
N
T
ce
Te
d
A
rra
re
ce
a
C
d
S
R
C
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T
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C
C
ea
S
on
C
to
T
u
C
rA
on
re
to
a
ur
C
S
R
F
N
T
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on
a
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t
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ou
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r
on
Ar
ea
to
ur
R
F
A
re
a
Ar
ea
T
N
C
S
R
F
T
C
C
S
C
S
Ar
e
Ar
ea
T
C
P
C
R
a
Focus on N
Focus on P and N
Ar
ea
Sq. km
Nodaway
Watershed distribution of options
Nodaway
Watershed distribution by practice
1200
1000
Sq. km
800
Focus on N
600
Focus on P, achieve both N and P
Baseline
400
200
0
CRP
CS CT
N reduction
No Till
Terrace
Contouring
40
Conclusions and Recommendations

Significant reductions in both phosphorus and nitrogen loadings
can be achieved in all of the watersheds in the state


The costs are significant
But, much smaller than they would be if didn’t carefully select which
practices go where (targeting)

Focus on N alone produces a markedly different watershed
configuration than when the focus is both on P and N

Practices which are efficient for phosphorus and erosion control
are, in general, not efficient in controlling nitrogen

If we wish to focus to both nutrients, combining traditional structural
practice with measures directly targeting nitrogen will be necessary
41
Caveats and Research Needs


Inclusion of other options will very likely alter results
Results needed to be interpreted with caution




E.g., we do not recommend actual removal of conservation
practices or abandonment of conservation tillage
Lack of detailed spatial data only allows identification
of desired conservation option mix at the subbasin
level
Better hydrologic, water quality, land use, and farm-level
data would help to add realism to the analysis
Studying sensitivity of the results to changes in costs,
efficiencies of conservation practices and weather
42
conditions would be very helpful in providing
Continuing Work

Sergey Rabotyagov’s PhD thesis, Iowa updates






UMRB work (also Sergey)
Smaller watershed work (field scale)



2007 land and corn prices
Added grassed waterways as an option
Continued improvements to SWAT
30% N and P reductions ~ $300 million/yr cost
Walnut Creek (CEAP project – USDA)
Boone (USDA-CSREES)
Application of GA for biofuels sustainability
43